BZOJ 1304: [CQOI2009]叶子的染色 树形DP + 结论

Code:

#include<bits/stdc++.h>
#define setIO(s) freopen(s".in","r",stdin)
#define maxn 1000000
#define inf 1000000000
using namespace std;
int n,m,edges;
int col[maxn],f[maxn][2],hd[maxn],to[maxn<<1],nex[maxn<<1];
void addedge(int u,int v)
{
    nex[++edges]=hd[u],hd[u]=edges,to[edges]=v;
}
void dfs(int u,int ff)
{
    if(u<=n) return;
    for(int i=hd[u];i;i=nex[i])
    {
        int v=to[i];
        if(v==ff) continue;
        dfs(v, u);
        f[u][0]+=min(f[v][0]-1,f[v][1]);
        f[u][1]+=min(f[v][1]-1,f[v][0]);
    }
}
int main()
{
    // setIO("input");
    int i,j;
    scanf("%d%d",&m,&n);
    for(i=1;i<=m;++i) f[i][0]=f[i][1]=1;
    for(i=1;i<=n;++i) scanf("%d",&col[i]), f[i][col[i]^1]=inf;
    for(i=1;i<m;++i)
    {
        int a,b;
        scanf("%d%d",&a,&b);
        addedge(a,b), addedge(b,a);
    }
    dfs(n+1,0);
    printf("%d\n",min(f[n+1][0], f[n+1][1]));
    return 0;
}